Ailawadi, Gorav Project Summary Aortic aneurysms (AA) are the 13th leading cause of death in the U.S. Since no medical therapy exists to alter the progression of disease, understanding the pathogenesis of AA is an important undertaking. The hallmark of AAs includes inflammatory infiltration, matrix metalloproteinase (MMP) production by macrophages and smooth muscle cells (SMCs) leading to destruction of collagen and elastin in the aortic wall and vessel dilation. Our preliminary data suggests that SMCs undergo phenotypic switching defined by increased SMC production of MMPs and downregulation of SMC contractile marker genes prior to experimental aneurysm formation. The loss of Kruppel like factor-4 (KLF4) has been shown to delay phenotypic switching to an inflammatory phenotype in a ligation-induced model of vascular injury. Moreover, in this model, KLF4 loss resulted in hyperproliferation of medial SMCs. KLF4 appears to have opposing effects in macrophages and endothelial cells. Preliminary studies in our lab have documented KLF4 is profoundly elevated in human and experimental aneurysms by immunohistochemistry. The focus of this proposal is to test the hypothesis that KLF4 plays a key role in experimental aneurysms and that effects are mediated through actions of KLF4 in SMCs, macrophages, and/ or endothelial cells. Aim 1 will determine if conditional KLF4 knockout mice show altered formation of aneurysms and if effects are mediated through effects in SMCs or in other cell types. We will utilize several unique transgenic knockout mice developed in the Owens (mentor's) lab as well as bone marrow reconstitution studies that will allow cell specific deletion of KLF4 and subject them to an experimental aneurysm formation using elastase perfusion. Aim 2 will determine if epigenetic mechanisms contribute to the effects of KLF4 on aortic aneurysm formation. Studies will test the hypothesis that KLF4 contributes to suppression of SMC marker genes and activation of several inflammatory genes within aneurysms, by binding to promoters in each of these genes, mediating histone modifications association with transcriptional silencing and activation. Finally, we will determine if these epigenetic modifications in AA are KLF4 dependent using KLF4 knockout mice. PHS 398/2590 (Rev. 11/07) Page Continuation Format Page